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Chapter: Anatomy and Physiology for Health Professionals: Lymphatic System and Immunity

The lymphatic system is related very closely to the cardiovascular system.


The lymphatic system is related very closely to the cardiovascular system. It transports excess tissue fluid to the bloodstream. It also absorbs fats and helps to defend against disease-causing agents. Lymphoid cells consist of the T and B lymphocytes, plasma cells, macrophages, dendritic cells, and reticular cells. Lymphoid tissue dominates nearly all lym-phoid organs and is mostly composed of reticular connective tissue. Lymph returns protein molecules to the bloodstream and transports foreign particles to lymph nodes. Along with the lymph nodes, the thymus and spleen are the predominant organs of the lymphatic system, along with tonsils, Peyer’s patches, and appendix.

Tissue fluid originates from blood plasma. Lymph forms from interstitial fluid and is called lymph when it enters the lymphatic vessels. Lymph moves toward the heart via the lymphatic capillaries and lacteals, collecting lymphatic vessels, and lymphatic trunks. The lymphatic trunks lead to two collecting ducts—the thoracic duct and the right lymphatic duct. The body has defenses that protect it against infection: innate, nonspecific defenses and adaptive, specific defenses. The adaptive specific defenses are also known as immunity. T cells and B cells reside in lymphatic tissues and organs and are vital for the body’s self-protection. Lymphocytes originate in red bone marrow and are released into the blood. Anti-bodies are gamma globulin proteins called immu-noglobulins and include five major types: IgG, IgA, IgM, IgD, and IgE. Naturally acquired immunity arises as a result of natural events, whereas artificially acquired immunity is caused by a medical procedure. Active immunity lasts much longer than passive immunity. The presence of allergens in the body can produce various types of allergies that the body may respond to either immediately or in a delayed man-ner. Another type of body reaction concerns rejec-tion of transplanted tissue.

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